- SharpCap 3.0, settings file attached.
- Celestron C8 on CG5 equatorial mount, TS f6.3 reducer/flattener, no filters.
- Mount alignment = polar scope (eyeball!), 2 star alignment + 4 calibration stars carried out with f6.3 reducer and camera fitted to telescope and SharpCap reticule turned on.
- Laptop LENOVO T400, CPU 2.4GHz Core 2 Duo, 8Gb RAM, 120Gb SSD, Windows 10 64-bit.
- 7 frames @ 30s exposure.
- Capture Area=1280x960.
- Colour Space=RAW16.
- Output to FITS file.
- Darks taken in SC but not applied during capture.
- Deep Sky Stacker - 7 lights + 1 dark stacked, RAW/FITS digital development process settings > FITS > debayered=GRBG, stacking=intersection mode, lights & darks Stacking Mode=Median Kappa-Sigma Clipping, output saved as TIFF image (32 bit/ch rational).
- GIMP v9.5 (can process 16-bit with no loss of data) - Levels & Curves, export as PNG.
- Nebulosity - star sharpening.
- FastStone Image Viewer - reduce image size and bit depth for upload to forum.
The (undocked) capture histogram:
- Camera setting Brightness adjusted to 10 to bring histogram away from left-hand side (ensures no data lost).
- Histogram hitting right-hand side. Looks like ~10 pixels over exposed so data loss is minimal.
- Colour balance acceptable.
- Classic histogram shape for a DSO using logarithmic vertical scale.
One of the 7 captures had a satellite passing through it. This was processed out (without intervention by me) during the stacking. I think the Median Kappa-Sigma clipping helped with that.
One of the FITS captures displayed in FITS Liberator. Notice the checked pattern - this is how a raw image looks before being debayered. The small bright green dots are hot pixels - which are removed when the dark frame is applied to the image. The histogram looks reasonable for a DSO. The nebula can be seen faintly in the centre - it is surprising that stacking only 7 x 30s images can produce the image at the top - I wonder what improvement using 100 or 500 images would make - one for the future?
The first attempt at post-processing was to debayer the frames using PIPP. I ended up with a green image even though I had chosen GRBG. This has worked before, so some sort of user error here which requires further investigation. I managed not to take any flat frames during the capture (a race against clouds/rain), which I did not find out about until the next day. I resolved this in GIMP by using the Clone/Stamp tool to remove the dust motes.
Here is my attempt at M27 taken around 1 year ago, same telescope/mount using an LN300 style video camera: So it looks like persistence is the key!
Things for me to try:
- Alternate stacking modes in Deep Sky Stacker (one for a cloudy night).
- Capturing and stacking more images at 30s.
- Capturing and stacking at 15s and 60s exposure.
- More practise with Levels and Curves in GIMP.
- Carry out the post-processing in Nebulosity (another one for a cloudy night).
- Repeat the capture with the video camera used last year.